Process for producing spheroidized powder from feedstock materials

ABSTRACT

Disclosed herein are embodiments of methods, devices, and assemblies for processing feedstock materials using microwave plasma processing. Specifically, the feedstock materials disclosed herein pertains to scrap materials, dehydrogenated or non-hydrogenated feed material, and recycled used powder. Microwave plasma processing can be used to spheroidize and remove contaminants. Advantageously, microwave plasma processed feedstock can be used in various applications such as additive manufacturing or powdered metallurgy (PM) applications that require high powder flowability.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/827,322, filed on Mar. 23, 2020, entitled “PROCESS FOR PRODUCINGSPHEROIDIZED POWDER FROM FEEDSTOCK MATERIALS,”, which is a continuationof U.S. application Ser. No. 16/446,445 filed on Jun. 19, 2019, entitled“PROCESS FOR PRODUCING SPHEROIDIZED POWDER FROM FEEDSTOCK MATERIALS,”now U.S. Pat. No. 10,639,712, issued May 5, 2020, which claims thepriority benefit of U.S. Provisional Patent Application Ser. No.62/687,109 entitled “Methods for Producing Spheroidized Powder From aDehydrogenated or Non-Hydrogenated Feed Material,” filed on Jun. 19,2018, U.S. Provisional Patent Application Ser. No. 62/687,094 entitled“Process for Recycling Used Powder to Produce Spheroidized Powder,”filed on Jun. 19, 2018, and U.S. Provisional Patent Application Ser. No.62/687,079 entitled “Process for Reusing Scrap Metal or Used Metal Partsfor Producing Spheroidized Powder,” filed on Jun. 19, 2018, the contentsof each of which are hereby incorporated by reference in theirentireties.

BACKGROUND Field

The present disclosure is generally directed in some embodiments towardsproducing metal spherical or spheroidal powder products from feedstockmaterials including from scrap materials, dehydrogenated ornon-hydrogenated materials, or recycled used powder.

Description of the Related Art

An important aspect of preparing some forms of industrial powders is thespheroidization process, which transforms irregularly shaped or angularpowders produced by conventional crushing methods, into sphericallow-porosity particles. Spherical powders are homogenous in shape,denser, less porous, have a high and consistent flowability, and hightap density. Such powders exhibit superior properties in applicationssuch as injection molding, thermal spray coatings, additivemanufacturing, etc.

Creating spheroidal metallic powders, especially metallic powderscontaining Ti, can pose a number of challenges. Achieving the desiredspheroidal shape, the desired level of porosity (e.g., no porosity tovery porous, and the desired composition and microstructure can bedifficult.

Conventional spheroidization methods employ thermal arc plasma describedin U.S. Pat. No. 4,076,640 issued Feb. 28, 1978 and radio-frequencygenerated plasma described in U.S. Pat. No. 6,919,527 issued Jul. 19,2005. However, these two methods present limitations inherent to thethermal non-uniformity of radio-frequency and thermal arc plasmas.

In the case of thermal arc plasma, an electric arc is produced betweentwo electrodes generates a plasma within a plasma channel. The plasma isblown out of the plasma channel using plasma gas. Powder is injectedfrom the side, either perpendicularly or at an angle, into the plasmaplume, where it is melted by the high temperature of the plasma. Surfacetension of the melt pulls it into a spherical shape, then it is cooled,solidified and is collected in filters. An issue with thermal arc plasmais that the electrodes used to ignite the plasma are exposed to the hightemperature causing degradation of the electrodes, which contaminatesthe plasma plume and process material. In addition, thermal arc plasmaplume inherently exhibit large temperature gradient. By injecting powderinto the plasma plume from the side, not all powder particles areexposed to the same process temperature, resulting in a powder that ispartially spheroidized, non-uniform, with non-homogeneous porosity.

In the case of radio-frequency inductively coupled plasmaspheroidization, the plasma is produced by a varying magnetic field thatinduces an electric field in the plasma gas, which in turn drives theplasma processes such as ionization, excitation, etc to sustain theplasma in cylindrical dielectric tube. Inductively coupled plasmas areknown to have low coupling efficiency of the radio frequency energy intothe plasma and a lower plasma temperature compared to arc and microwavegenerated plasmas. The magnetic field responsible for generating theplasma exhibits a non-uniform profile, which leads to a plasma with alarge temperature gradient, where the plasma takes a donut-like shapethat exhibiting the highest temperature at the edge of the plasma (closeto the dielectric tube walls) and the lowest temperature in the centerof the donut. In addition, there is a capacitive component createdbetween the plasma and the radio frequency coils that are wrapped aroundthe dielectric tube due to the RF voltage on the coils. This capacitivecomponent creates a large electric field that drives ions from theplasma towards the dielectric inner walls, which in turn leads to arcingand dielectric tube degradation and process material contamination bythe tube's material.

To be useful in additive manufacturing or powdered metallurgy (PM)applications that require high powder flow, metal powder particlesshould exhibit a spherical shape, which can be achieved through theprocess of spheroidization. This process involves the melting ofparticles in a hot environment whereby surface tension of the liquidmetal shapes each particle into a spherical geometry, followed bycooling and re-solidification. Also, spherical powders can be directlyproduced by various techniques. In one such technique, a plasma rotatingelectrode (PRP) produces high flowing and packing titanium and titaniumalloy powders but is deemed too expensive. Also, spheroidized titaniumand titanium alloys have been produced using gas atomization, which usesa relatively complicated set up and may introduce porosity to thepowder. Spheroidization methods of irregular shape powders includeTEKNA's (Sherbrook, Quebec, Canada) spheroidization process usinginductively coupled plasma (ICP), where angular powder obtained fromHydride-Dehydride (HDH) process is entrained within a gas and injectedthrough a hot plasma environment to melt the powder particles. However,this method suffers from non-uniformity of the plasma, which leads toincomplete spheroidization of feedstock. The HDH process involvesseveral complex steps, including hydrogenation dehydrogenation, anddeoxydation before the powder is submitted to spheroidization. Thisprocess is a time consuming multi-step process, which drives up the costof metal powders made through these methods.

SUMMARY

Disclosed herein are embodiments of a method for manufacturing aspheroidized powder from scrap metal or used metal parts, the methodcomprising: providing scrap metal or used metal parts comprising amaterial selected from the group consisting of metal, metal alloy,titanium, titanium alloy, nickel, nickel alloy, cobalt, cobalt alloy,steel, and steel alloy; milling the scrap metal or used metal parts toproduce metallic particles within a range of particle volumespre-determined to be suitable for use as feedstock in a microwave plasmaprocess; and applying the microwave plasma process to the metallicparticles within the determined range of particle volumes to formspheroidized powder.

In some embodiments, the determined range of particle volumes can bebetween 15 and 63 microns. In some embodiments, the scrap metal or usedmetal parts can comprise a work hardened microstructure that is retainedin the spheroidized powder after applying the microwave plasma process.In some embodiments milling the scrap metal or used metal parts can bedone without embrittling the scrap metal or used metal parts.

In some embodiments, the scrap metal or used metal parts can comprise Ti6Al-4V. In some embodiments the scrap metal or used metal parts cancomprise alloy elements including Al, Mg, Ti, and/or Cu and, afterapplying the microwave plasma process the spheroidized powder stillincludes the Al, Mg, Ti, and/or Cu. In some embodiments, the scrap metalor used metal parts can comprise sharp turnings, saw swarfs, grindingswarfs, grinding fines, and/or wash line fines. In some embodiments, thescrap metal or used metal parts can be selected for the milling to havea size and/or aspect ratio that will result post-milling in metallicparticles within the pre-determined range of particle volumes.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder having a desired particle size distribution betweenabout x and about y, wherein x represents a low end of the particle sizedistribution and y represents a high end of the particle sizedistribution, the method comprising: introducing metallic particlesobtained by milling or crushing scrap metal or used metal parts into amicrowave plasma torch, a majority of said introduced metallic particleshaving a volume between about 4/3 π (x/2)³ and about 4/3 π (y/2)³, andwherein said introduced metallic particles have a collective average ormedian aspect ratio between 2:1 and 200:1; and melting and spheroidizingthe metallic particles within the microwave plasma torch to formspheroidized powder having the desired particle size distribution ofabout x to about y.

In some embodiments x can equal 5 microns and y can equal 45 microns andthe majority of said introduced metallic particles can have a volumebetween about 65.45 μm³ and about 47,712.94 μm³. In some embodiments,the collective average or median aspect ratio can be between 5:1 to20:1. In some embodiments, the collective average or median aspect ratiocan be between 10:1 to 100:1. In some embodiments, the introducingmetallic particles into the microwave plasma torch can compriseintroducing the metallic particles into an exhaust of the microwaveplasma torch or into a plume of the microwave plasma torch.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder from scrap metal or used metal parts, the methodcomprising: introducing metallic particles obtained by milling orcrushing scrap metal or used metal parts into a microwave plasma torch;and melting and spheroidizing the metallic particles within themicrowave plasma torch to form spheroidized powder.

In some embodiments, the milled or crushed particles can have a desiredparticle size distribution. In some embodiments, the desired particlesize distribution can be 15 to 63 microns. In some embodiments, themilled or crushed particles can have a desired range of particlevolumes. In some embodiments, the particles can be milled or crushedwithout embrittling the scrap metal or used metal parts. In someembodiments, milling or crushing the scrap metal or used metal parts canbe used to produce the metallic particles.

In some embodiments, the scrap metal or used metal parts can comprisetitanium or titanium alloy. In some embodiments, the scrap metal or usedmetal parts can comprise nickel or nickel alloy. In some embodiments,the scrap metal or used metal parts can comprise cobalt or cobalt alloy.In some embodiments, the scrap metal or used metal parts can comprisesteel or steel alloy. In some embodiments, the scrap metal or used metalparts can comprise a ductile metal or metal alloy.

In some embodiments, the metallic particles can comprise milled turningsresulting from subtractive manufacturing. In some embodiments, the scrapmetal or used metal parts can comprise sharp turnings, saw swarfs,grinding swarfs, grinding fines, and/or wash line fines. In someembodiments, the metallic particles can comprise a work hardenedmicrostructure that is at least partially retained after the melting andspheroidizing. In some embodiments, the metallic particles can be onlypartially surface melted.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder from scrap metal or used metal parts, the methodcomprising: providing scrap metal or used metal parts comprisingtitanium, titanium alloy or other ductile metal or ductile metal alloy;milling the scrap metal or used metal parts to produce metallicparticles within a range of particle volumes pre-determined to besuitable for use as feedstock in a microwave plasma process, wherein thescrap metal or used metal parts are selected for the milling to have asize and/or aspect ratio that will result post-milling in metallicparticles within the pre-determined range of particle volumes, whereinthe milling occurs without embrittling the scrap metal or used metalparts; and applying the microwave plasma process to the metallicparticles within the determined range of particle volumes to formspheroidized powder.

In some embodiments, the method can further comprise selecting portionsof the scrap metal or used metal parts having a size and/or aspect ratiosuitable for milling to the determined range of particle volumes. Insome embodiments, the determined range of particle volumes can bebetween 15 and 63 microns. In some embodiments, the scrap metal or usedmetal parts comprise a work hardened microstructure that is retained inthe spheroidized powder after applying the microwave plasma process.

In some embodiments, the milling can be performed in water. In someembodiments, the method can further comprise processing the spheroidizedpowder in an additive manufacturing process. In some embodiments, themethod can further comprise milling the scrap metal or used metal partswithout embrittling the scrap metal or used metal parts by hydrogenationor applying cryogenics. In some embodiments, the scrap metal or usedmetal parts can comprise turnings resulting from subtractivemanufacturing.

In some embodiments, the scrap metal or used metal parts can compriseTi-6-4. In some embodiments, the spheroidized powder resulting from theprocesses above.

Also disclosed herein are embodiments of a method of laser bed fusion,comprising using the spheroidized powder resulting from one or morefeatures of the description above.

Also disclosed herein are embodiments of a method of electron beammanufacturing, comprising using the spheroidized powder resulting fromone or more features of the description above.

Also disclosed herein are embodiments of a method of metal injectionmolding, comprising using the spheroidized powder resulting from one ormore features of the description above.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder from scrap metal or used metal parts, the methodcomprising: providing scrap metal or used metal parts; milling the scrapmetal or used metal parts to produce metallic particles within a rangeof particle volumes pre-determined to be suitable for use as feedstockin a microwave plasma process, wherein the scrap metal or used metalparts are selected for the milling to have a size and/or aspect ratiothat will result post-milling in metallic particles within thepre-determined range of particle volumes, wherein the milling occurswithout embrittling the scrap metal or used metal parts; and applyingthe microwave plasma process to the metallic particles within thedetermined range of particle volumes to form spheroidized powder.

Also disclosed herein are embodiments of a spheroidized powdermanufactured according to the methods described above.

Further disclosed herein are embodiments of a method for manufacturing aspheroidized powder from used powder, the method comprising: introducingpreviously used powder particles into a microwave plasma torch; andmelting and spheroidizing the previously used powder particles withinthe microwave plasma torch to form spheroidized powder particles.

In some embodiments, the previously used powder particles can have adesired particle size distribution. In some embodiments, the previouslyused powder particles can comprise satellites, wherein the satellitescan be removed during the melting and spheroidizing. In someembodiments, the previously used powder particles can compriseagglomerations, wherein the agglomerations can be removed during themelting and spheroidizing. In some embodiments, the previously usedpowder particles can comprise contaminants, wherein the contaminants canbe removed during the melting and spheroidizing.

In some embodiments, the previously used powder particles can comprisemetal or metal alloys. In some embodiments, the previously used powderparticles can comprise titanium or titanium alloy. In some embodiments,the previously used powder particles can comprise nickel or nickelalloy. In some embodiments, the previously used powder particles cancomprise a ductile metal or metal alloy. In some embodiments, thepreviously used powder particles can comprise cobalt or cobalt alloy. Insome embodiments, the previously used powder particles can comprisesteel and steel alloy. In some embodiments, the previously used powderparticles can comprise a ceramic.

In some embodiments, the melting and spheroidizing can improveflowability of the previously used powder particles. In someembodiments, the melting and spheroidizing can increase density of thepreviously used powder particles. In some embodiments, carbon, nitrogenand/or other contaminants can be removed from the previously used powderparticles during the melting and spheroidizing.

In some embodiments, a noble gas, argon gas, a mixture of argon gas andhydrogen gas, or nitrogen gas can be used during the melting andspheroidizing. In some embodiments, the previously used powder particlescan be formed from an additive manufacturing process. In someembodiments, the additive manufacturing process can comprise lasersintering, electron-beam melting, filament fused deposition, directedenergy deposition, powder bed fusion, or binder jetting.

In some embodiments, the spheroidized powder particles can retain thesame rheological properties as the previously used powder particlesafter the melting and spheroidizing. In some embodiments, alloycomponent chemistry and/or minor component chemistry being less than 10wt % can be the same in the spheroidized powder particles as thepreviously used powder particles. In some embodiments, the previouslyused powder particles can substantially only comprise particles that arenot spheroidal. In some embodiments, the previously used powderparticles can substantially only comprise particles that havesatellites, contaminants, and/or agglomerations. In some embodiments,the previously used powder particles can comprise particles that are notspheroidal and particles that are spheroidal without having anysatellites, contaminants, and/or agglomerations.

Further disclosed herein are embodiments of a method for producing aspheroidized powder from a feed material comprising dehydrogenated ornon-hydrogenated titanium or titanium alloy, the method comprising:introducing a feed material comprising dehydrogenated ornon-hydrogenated titanium or titanium alloy particles into a microwaveplasma torch; and melting and spheroidizing the particles within aplasma generated by the microwave plasma torch to form spheroidizedpowder.

In some embodiments, the feed material can comprise titanium or titaniumalloy particles processed by the hydrogenation-dehydrogenation (HDH)process. In some embodiments, the spheroidized powder can compriseparticles with a median sphericity of at least 0.75. In someembodiments, the spheroidized powder can comprise particles with amedian sphericity of at least 0.91. In some embodiments, thespheroidized powder can have a particle size distribution of 15 to 45microns. In some embodiments, the spheroidized powder can have aparticle size distribution of 45 to 105 microns.

In some embodiments, the method can further comprise exposing thespheroidized particles to an inert gas. In some embodiments, the methodcan further comprise setting one or more cooling processing variables totailor the microstructure of the spheroidized particles. In someembodiments, setting one or more cooling processing variables cancomprise selecting and controlling a cooling gas flow rate. In someembodiments, setting one or more cooling processing variables cancomprise selecting and controlling a residence time of the particles offeed materials within the plasma. In some embodiments, setting one ormore cooling processing variables can comprise selecting and controllinga cooling gas composition. In some embodiments, the cooling gascomposition can be selected to provide high thermal conductivity.

In some embodiments, one or more cooling processing variables can be setto create a martensitic microstructure in the spheroidized particles. Insome embodiments, one or more cooling processing variables can be set tocreate a Widmanstätten microstructure in the spheroidized particles. Insome embodiments, one or more cooling processing variables can be set tocreate an equiaxed microstructure in the spheroidized particles. In someembodiments, one or more cooling processing variables can be set tocreate at least two regions, each region having a differentmicrostructure. In some embodiments, the at least two regions caninclude a core portion and a skin portion. In some embodiments, the skinportion can have a microstructure that is different from the feedmaterial's microstructure.

In some embodiments, melting and spheroidizing of the particles canoccur within a substantially uniform temperature profile between about4,000K and 8,000K. In some embodiments, the feed material can have aparticle size of no less than 1.0 microns and no more than 300 microns.In some embodiments, the feed material can comprise Ti-6-4, and themelting and spheroidizing can be controlled such that the spheroidizedpowder comprises Ti-6-4.

Also disclosed herein are embodiments of a spheroidized powdermanufactured according to the methods disclosed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example embodiment of scrap metal feedstock in theform of metal turnings before microwave plasma processing according tothe present disclosure.

FIG. 2 illustrates an example embodiment of scrap metal feedstock in theform of metal turnings after microwave plasma processing according tothe present disclosure.

FIG. 3 illustrates an example of a plot of L/W (aspect ratio) for asample of metal turnings before microwave plasma processing according tothe present disclosure.

FIG. 4 illustrates an example embodiment of a method for reusing scrapmetal/alloys using microwave plasma processing according to the presentdisclosure.

FIG. 5 illustrates an example embodiment of a method for processinghydride-dehydride (HDH) produced feedstock using microwave plasmaprocessing according to the present disclosure.

FIG. 6 and FIG. 7 illustrate example embodiments of used powder CoCrfeedstock before microwave plasma processing according to the presentdisclosure.

FIG. 8 and FIG. 9 illustrate example embodiments of used powder CoCrfeedstock after microwave plasma processing according to the presentdisclosure.

FIG. 10 illustrates an example embodiment of a method of producingspheroidal particles according to the present disclosure.

FIG. 11 illustrates an embodiment of a microwave plasma torch that canbe used in the production of spheroidal metal or metal alloy powders,according to embodiments of the present disclosure.

FIGS. 12A-B illustrate embodiments of a microwave plasma torch that canbe used in the production of spheroidal metal or metal alloy powders,according to a side feeding hopper embodiment of the present disclosure.

FIG. 13 illustrates an example embodiment of a method of producingtitanium based (e.g., titanium, titanium alloy) spheroidal particleshaving a desired microstructure according to the present disclosure.

FIG. 14 illustrates an example embodiment of a method of modifying aparticle microstructure according to embodiments of the presentdisclosure.

FIG. 15 illustrates an embodiment of a particle modified according toembodiments of the present disclosure.

DETAILED DESCRIPTION

Disclosed herein are embodiments of methods, devices, and assemblies forspheroidization of feedstock materials using microwave plasmaprocessing. Each different feedstock material has its own critical,specialized, and unique requirements for the initial feedstock as wellas the processing in a microwave plasma torch in order to achieve adesired spheroidization. Specifically, the feedstock materials disclosedherein pertain to scrap materials, dehydrogenated or non-hydrogenatedfeed material, and recycled used powder, the feedstocks which mayrequire initial pre-processing or specific plasma processing. Asdisclosed herein, processing in a microwave plasma torch can includefeeding the feedstock into a microwave plasma torch, a plasma plume ofthe microwave plasma torch, and/or an exhaust of the microwave plasmatorch. The location may vary depending on the type of feedstock used.Further the feedstock can be selected based on different requirements.Examples of requirements are aspect ratio, particle size distribution(PSD), chemistry, density, diameter, sphericity, oxygenation, hardness,and ductility.

Scrap Materials

Disclosed herein are embodiments of methods, devices, and assemblies forreusing scrap metals/alloys and/or used parts made from metals/alloys(e.g., grave-to-cradle or scrap to premium). In particular, embodimentsof the disclosure allow for taking metallic scrap or used metal parts,such as turnings, and without embrittling (such as through the use ofhydrogenation or cryogenics) creating a feedstock for a microwave plasmaprocess. Specifically, scrap or used metal parts can be milled to adesired volume of particles of a feedstock or turnings, though in someembodiments may not be milled. The feedstock or turnings can then beused as a feedstock for a microwave plasma process to form a finalspheroidized powder, which can then be used in different processes, suchas additive manufacturing processes. However, scrap material isextremely difficult to process into a proper feedstock for microwaveplasma processing.

In some embodiments the method can include an analysis of theinter-relationship between 1) selection of feedstock size/aspect ratio,2) a milling approach that breaks up ductile pieces without embrittlingsteps, and 3) a final desired particle volume, in order to create adesired particle size distribution for specific applications. In someembodiments, the feedstock is embrittled before milling. A user canspecify a desired particle volume for the milling of the original scrap,which will influence the selection of the feedstock size/aspect ratioand the milling approach utilized.

The final specific application can be, for example, laser bed fusionwhich has a particle size distribution (PSD) of 15-45 microns (or about15 to about 45 microns), or 15-63 microns (or about 15 to about 63microns) or 20-63 microns (or about 20-about 63 microns), electron beamprocessing which can have a particle size distribution of 45-105 microns(or about 45 to about 105 microns) or 105-150 microns (or about 105 toabout 150 microns), or metal injection molding (MIM). In someembodiments, the PSD can be expressed as the D50 of the particles in thefeedstock. In some embodiments, the feedstock is processed through jetmilling, wet milling, or ball milling. In some embodiments, the PSD ofthe feedstock is 15-15 microns, 15-45 microns, 20-63 microns, 45-105microns, or 105 to 150 microns. The PSD can be adjusted depending on thepowder processing technology such as laser powder bed fusion, directenergy deposition, binder jet printing, metal injection molding, and hotisostatic pressing.

The original scrap or used metal parts can be sharp turnings (e.g.,having high aspect ratio, high surface area, thin, or spaghetti-likematerial, scrap aggregator), saw swarf (high aspect ratio, thinmaterial), grinding swarf (less aspect ratio powder like material),grinding fines, or wash line fines (less aspect ratio, thick or thinplate like material) which can then be broken up into a feedstock of aparticular PSD, such as in a milling process, and then microwave plasmaprocessing this feedstock into spherical and dense powders. In someembodiments, the scrap can be 3D printed parts (such as failed 3Dprinted parts) or castings (such as failed castings). In someembodiments, the input materials can be wash line fine, saw swarfs,grinding swarfs. In some embodiments, the input materials can be used orscrap parts by processes like but not limited to grinding, milling,cutting, or turning. FIG. 1 is an illustrative example of metal turningfeedstock before plasma processing. FIG. 2 depicts the illustrativeexample of metal turnings after plasma processing.

In some embodiments, high aspect ratio turnings from machining processesare used as feedstock into the microwave plasma melting process toproduce spherical powders. In some embodiments, the average aspect ratioof the turnings is 2:1 (or about 2:1), 3:1 (or about 3:1), 5:1 (or about5:1), 10:1 (or about 10:1), 20:1 (or about 20:1), 100:1 (or about100:1), or 200:1 (or about 200:1). In some embodiments, the averageaspect ratio of the turnings is greater than 1:1 (or about 1:1), 3:1 (orabout 3:1), 5:1 (or about 5:1), greater 10:1 (or about 10:1), greater20:1 (or about 20:1), greater 100:1 (or about 100:1), or greater 200:1(or about 200:1). In some embodiments, the average aspect ratio of theturnings is less than, 3:1 (or about 3:1), 5:1 (or about 5:1), greater10:1 (or about 10:1), greater 20:1 (or about 20:1), greater 100:1 (orabout 100:1), or greater 200:1 (or about 200:1).

In some embodiments, the aspect ratio of a majority of the turnings is2:1 (or about 2:1), 3:1 (or about 3:1), 5:1 (or about 5:1), 10:1 (orabout 10:1), 20:1 (or about 20:1), 100:1 (or about 100:1), or 200:1 (orabout 200:1). In some embodiments, the aspect ratio of a majority of theturnings is greater than 1:1 (or about 1:1), 3:1 (or about 3:1), 5:1 (orabout 5:1), greater 10:1 (or about 10:1), greater 20:1 (or about 20:1),greater 100:1 (or about 100:1), or greater 200:1 (or about 200:1). Insome embodiments, the aspect ratio of a majority of the turnings is lessthan, 3:1 (or about 3:1), 5:1 (or about 5:1), greater 10:1 (or about10:1), greater 20:1 (or about 20:1), greater 100:1 (or about 100:1), orgreater 200:1 (or about 200:1).

In some embodiments, the aspect ratio of greater than 75% of theturnings is 2:1 (or about 2:1), 3:1 (or about 3:1), 5:1 (or about 5:1),10:1 (or about 10:1), 20:1 (or about 20:1), 100:1 (or about 100:1), or200:1 (or about 200:1). In some embodiments, the aspect ratio of greaterthan 75% of the turnings is greater than 1:1 (or about 1:1), 3:1 (orabout 3:1), 5:1 (or about 5:1), greater 10:1 (or about 10:1), greater20:1 (or about 20:1), greater 100:1 (or about 100:1), or greater 200:1(or about 200:1). In some embodiments, the aspect ratio of greater than75% of the turnings is less than, 3:1 (or about 3:1), 5:1 (or about5:1), greater 10:1 (or about 10:1), greater 20:1 (or about 20:1),greater 100:1 (or about 100:1), or greater 200:1 (or about 200:1).

In some embodiments, the aspect ratio of greater than 90% of theturnings is 2:1 (or about 2:1), 3:1 (or about 3:1), 5:1 (or about 5:1),10:1 (or about 10:1), 20:1 (or about 20:1), 100:1 (or about 100:1), or200:1 (or about 200:1). In some embodiments, the aspect ratio of greaterthan 90% of the turnings is greater than 1:1 (or about 1:1), 3:1 (orabout 3:1), 5:1 (or about 5:1), greater 10:1 (or about 10:1), greater20:1 (or about 20:1), greater 100:1 (or about 100:1), or greater 200:1(or about 200:1). In some embodiments, the aspect ratio of greater than90% of the turnings is less than, 3:1 (or about 3:1), 5:1 (or about5:1), greater 10:1 (or about 10:1), greater 20:1 (or about 20:1),greater 100:1 (or about 100:1), or greater 200:1 (or about 200:1).

In some embodiments, the feedstock is tailored to have a volumedistribution approximately equal to the volume distribution of thedesired PSD of processed powder. Volume is calculated based on 4/3*π*r³where ‘r’ is the radius of the processed powder. In some embodiments, amajority of the feedstock particles have a volume within a range ofabout 4/3 π (x/2)³ and about 4/3 π (y/2)³, wherein x is the low end ofthe desired particle size distribution and y is the high end of thedesired particle size distribution. In some embodiments, substantiallyall of the feedstock particles have a volume within a range of about 4/3π (x/2)³ and 4/3 π (y/2)³. In one example, the volume distribution ofthe preprocessed and processed feedstock can be between about 65.45 μm³and about 47,712.94 μm³, corresponding to a desired particle sizedistribution of 5 to 15 microns for the processed powder. In someembodiments, an average or median aspect ratio, collectively, ofpreprocessed feedstock can be between 2:1 and 200:1, between 3:1 and200:1, between 4:1 and 200:1, or between 5:1 and 200:1. However, any ofthe disclosed ratios/diameters can be used for the volume calculation.After processing, the particle size distribution in one example can be 5to 45 microns. Other particle size distributions are also contemplated,including but not limited to particle size distributions of between 5and 45 microns at a low end of the particle size distribution range andbetween 15 and 105 microns at a high end of the particle sizedistribution range (e.g., 5 to 15 microns, 15 to 45 microns, 45 to 105microns).

In some embodiments, the volume distribution of the feedstock can be thesame as the final spheroidized powder. In some embodiments, the overallvolume of the feedstock can be the generally the same as the finalspheroidized powder. In some embodiments, the overall volume of thefeedstock can be within 1%, 2%, 3%, 4%, 5%, 10%, 15%, or 20% (or about1%, about 2%, about 3%, about 4%, about 5%, about 10%, about 15%, orabout 20%) of the final spheroidized powder.

In some embodiments, the feedstock may be generally spherical, orgenerally non-spherical. For example, the feedstock can be misshapenfeedstock, cubes, filaments, wires, etc.

These aspect ratios are merely exemplary and other aspect ratios can beused as well. FIG. 3 is an illustrative example of a sample of highaspect ratio turnings. In this figure, L/W (aspect ratio) is plotted forevery individual particle in a sample of high aspect ratio turnings.Aspect ratio is shown as L/W. As can be seen, the aspect ratios rangefrom around 1:1 to 15:1 with most of the particles falling between 1:1to 7:1. However, this is merely one example, and other aspect ratios canbe used as well.

Turnings from machining processes can be first collected, cleaned fromthe machining oils and other impurities, and then sieved to separatesmall particles/turnings that can directly be used as feedstock fromlarges ones that need further processing to reduce their size. Anexample method for further reducing the size of the turnings to thedesired sizes is through milling. The product of this milling process isthen sieved again into different sizes and the desired size is selectedto be used as feedstock for spheroidization. The materials to be usedcan be selected from any subtractive process that uses metal and metalalloys stock to produce parts.

More specifically, in some embodiments, the scrap may be pre-processedbefore they are introduced into the plasma process. For example, thescrap may be sieved to remove large agglomerations and selected to thedesired size to be processed in the plasma. In some embodiments, thescrap may be cleaned with water, surfactant, detergent, solvent or anyother chemical such as acids to remove contamination. In someembodiments, the scrap may be magnetically cleaned if they arecontaminated with any magnetic material. In some embodiments, thecleaning removes contaminants such as ceramics and oils. In someembodiments, the scrap can be pre-treated to de-oxidize it. In someembodiments, other elements or compounds can be added to compensate ormodify the chemistry of the used parts. In some embodiments, the scrapcan be de-dusted to remove fines. In some embodiments, no pre-processingmay be performed. All of these pre-processing techniques can also beused on the post-milled scrap feedstock.

In some embodiments, the material to be milled can be titanium ortitanium alloys. Specific titanium that can be used is commercially puretitanium (CpTi) (known as CpTi), TiAl, Ti-6Al-4V (Ti-6-4), and theparticular titanium material/alloy does not limit the disclosure.Titanium can be particular problematic for milling as it is highlyductile, and thus would merely bend or change shape, and would not bebroken down properly into a powder without embrittling, such as throughhydrogenation or cryogenics. However, embodiments of the disclosure canmill titanium or titanium alloys without such an embrittling process.This can be done through the understanding and proper selection of thescrap material to be milled, such as by only choosing material having aparticular volume/size/aspect ratio.

FIG. 4 is an illustrative example of a flow chart of a process 100 forreusing scrap metal/alloys. At block 102, the metal/alloy scraps can bereceived. In some embodiments, the metal/alloy scraps can be turnings,wash line fine, saw swarfs, grinding swarfs. The scrap metal/alloys canbe used or scrap parts by processes like but not limited to grinding,milling, cutting, or turning. At block 104 the metal/alloy scraps can becleaned. In some embodiments, the cleaning is with water, surfactant,detergent, solvent or any other chemical such as acids to removecontamination. In some embodiments, the cleaning removes machining oilsand other impurities. In some embodiments, cleaning is not necessary.

At block 106/108, the metal/alloy scraps can be sieved in order to sortbetween pieces that are too large and pieces that are small enough to beused as feedstock. If the pieces are small enough to be used asfeedstock they can pass to block 112. If the pieces are too large, theycan be milled at block 110 into smaller scrap metal/alloys in order toadjust particle size. In some embodiments, the milling can be jetmilling, wet milling, and/or ball milling. Block 106 can be repeated inorder to additionally sieve the milled scrap metal/alloys.Alternatively, it can be decided that the milled scrap metal/alloys areready to be used as feedstock at block 112.

At block 112/114, the milled scrap metal/alloy that is ready to use asfeedstock can be microwave plasma processed. Microwave plasma processingis described below and is also shown in FIG. 11 and FIGS. 12A-B.

As discussed above, scrap material may be extremely complicated toprepare for a feedstock.

Dehydrogenated or Non-Hydrogenated Feed Material

One aspect of the present disclosure involves a process ofspheroidization of metals and metal alloy using a microwave generatedplasma. The process uses readily available existing pre-screened ornon-prescreened raw materials made of metal and/or metal alloys asfeedstock. The powder feedstock is entrained in inert and/or reducingand/or oxidizing gas environment and injected into the microwave plasmaenvironment. Upon injection into a hot plasma, the feedstock isspheroidized and released into a chamber filled with an inert gas anddirected into hermetically sealed drums where is it stored. This processcan be carried out at atmospheric pressure, in a partial vacuum, or at aslightly higher pressure than atmospheric pressure. In alternativeembodiments, the process can be carried out in a low, medium, or highvacuum environment. The process can run continuously and the drums arereplaced as they fill up with spheroidized metal or metal alloyparticles. Furthermore, provided the homogeneity of the microwave plasmaprocess, particle agglomeration is also reduced, if not totallyeliminated, thus leading to at least maintaining the particle sizedistribution of the original feed materials. However, it can bechallenging to obtain the proper feedstock sizing because feedstock sizecriteria can be stringent. Different processing methods can be used toobtain different feedstock size criteria.

In some embodiments, a hydride-dehydride (HDH) process can be used toresize large metallic or metallic alloy pieces down to a finer particlesize distribution through crushing, milling, and screening. Metal andalloy powders can be manufactured using the HDH process, where bulkfeedstock, such as coarse metal powders or metal/metal alloy scraps,etc., are heated in a hydrogen-containing atmosphere at high temperature(˜700° C.) for a few days. This leads to the formation of a brittlemetal hydride, which can readily be crushed into a fine power and siftedto yield a desired size distribution determined by the end user. To beuseful in powdered metallurgy, hydrogen must be dissociated and removedfrom the metal by heating the metal hydride powder within vacuum for aperiod of time. The dehydrogenated powder must then be sifted to removelarge particle agglomerations generated during process due to sintering.The typical resulting powder particles have an irregular or angularshape. The powder is submitted to a deoxidation process to remove anyoxygen picked up by the powder during sifting and handling. Such HDHprocesses produce only coarse and irregular shaped particles. Such HDHprocesses must be followed by a spheroidization process, such asdisclosed herein regarding a microwave plasma process, to make theseparticles spheroidal.

Embodiments of the disclosed HDH processes are primarily carried out assolid-state batch processes. A volume of metal powder can be loaded intoa crucible(s) within a vacuum furnace. The furnace can be pumped down toa partial vacuum and is repeatedly purged with inert gas to eliminatethe presence of undesired oxygen. Diffusion of the inert gas through theopen space between the powder particles is slow making it difficult tofully eliminate oxygen, which otherwise contaminates the final product.Mechanical agitation may be used to churn powder allowing for morecomplete removal of oxygen.

Following oxygen purging the, hydrogenation may begin. The furnace isfilled with hydrogen gas and heated up to a few days at high temperatureto fully form the metal hydride. The brittle nature of the metal hydrideallows the bulk material to be crushed into fine powders which are thenscreened into desired size distributions.

The next step is dehydrogenation. The screen hydride powder is loadedinto the vacuum furnace then heated under partial vacuum, promotingdissociation of hydrogen from the metal hydride to form H₂ gas anddehydrided metal. Dehydrogenation is rapid on the particle surface whereH₂ can readily leave the particles. However, within the bulk of thepowder, H₂ must diffuse through the bulk of the solid before it reachessurface and leave the particle. Diffusion through the bulk is arate-limiting process “bottle-neck” requiring relatively long reactiontime for complete dehydrogenation. The time and processing temperaturesrequired for dehydrogenation are sufficient to cause sintering betweenparticles, which results in the formation of large particleagglomerations in the final product. Post-process sifting can eliminatethe agglomerations. Before the powder can be removed from the furnace,it can be sufficiently cooled to maintain safety and limitcontamination. The thermal mass of the large furnaces may take minutesor hours to sufficiently cool. The cooled powders can then bespheroidized in a separate machine. In some embodiments, the feedstockmay be a non-hydrogenated material. In some embodiments, the materialhasn't undergone HDH but starts without any hydrogenation. In someembodiments, this can be carried out within the disclosed plasmaprocess.

FIG. 5 illustrates an embodiment of producing spheroidized titaniumpowder (200) from an HDH feed. The process flow (201) on the left ofFIG. 5 presents an example process that combines a HDH process (200)with spheroidization of titanium powders. The process starts with Ti rawmaterial (step a, 205) that is hydrogenated (step b, 210), and thencrushed and sifted to size (step c, 215). Pure titanium is recoveredthrough dehydrogenation (step d, 220). It is then screened foragglomerations and impurities, and then sifted to the size specified bythe customer (step e, 225). The powder then goes through a deoxidationstep to reduce or eliminate oxygen that it picked up during the siftingand screening processes. Deoxidation is useful especially for smallparticle sizes, such as particles below 50 microns, where the surface tovolume ratio is substantial (step f, 230). The titanium particles arethen spheroidized (step g, 235) and collected (step h, 240). A similarprocess can be used to create a Ti alloy, such as Ti 6-4, instead ofpure titanium powder.

In some embodiments, the powder is entrained within an inert gas andinjected into a microwave generated plasma environment (235) exhibitinga substantially uniform temperature profile between approximately 4,000K and 8,000 K and under a partial vacuum. The hermetically sealedchamber process can also run at atmospheric pressure or slightly aboveatmospheric pressure to eliminate any possibility for atmospheric oxygento leak into the process. The particles are melted in the plasma,spheroidized due to liquid surface tension, re-solidifying after exitingthe plasma. The particles are then collected in sealed drums in an inertatmosphere (140). Within the plasma, the powder particles can be heatedsufficiently to melt and cause convection of the liquid metal, causingdissociation of the hydrogen (if any remains after the HDH process)according to the reversible reaction where M=an arbitrary metal:

$\left. {M_{x}H_{y}}\leftrightarrow{{(x)M} + {\left( \frac{y}{2} \right)H_{2}}} \right.$

Within the partial vacuum, dissociation of hydrogen from the metal toform hydrogen gas is favored, driving the above reaction to the right.The rate of dissociation of hydrogen from the liquid metal is rapid, dueto convection, which continually introduces H₂ to the liquid surfacewhere it can rapidly leave the particle.

As discussed above, feedstock sizing can be difficult to obtain. An HDHprocess can aid in the process of obtaining feedstock that meets certainsize criteria.

Recycling Used Powder

Disclosed herein are embodiments of methods, devices, and assemblies forrecycling/reusing/reconditioning used powders (e.g., waste byproducts),such as from post processing or yield loss. In particular, embodimentsof the disclosure allow for the taking of used powder and converting itinto a feedstock for a microwave plasma process to form a finalspheroidized powder, which can then be used in different processes, suchas additive manufacturing processes, metal injection molding (MIM), orhot isostatic Pressing (HIP) processes. Thus, in some embodiments largeand/or misshapen particles can be re-spheroidized. Used powder can be ofdiffering quality and therefore it can be challenging to make use ofused powder as feedstock. The feedstock can be contaminated or anincorrect size, or altogether difficult to process.

In some embodiments, the powders may be pre-processed before they areintroduced into the plasma process. For example, the powders may besieved to remove large agglomerations and selected the desired size tobe processed in the plasma. In some embodiments, the powders may becleaned with water, surfactant, detergent, solvent or any other chemicalsuch as acids to remove contamination. In some embodiments, the powdersmay be magnetically cleaned if they are contaminated with any magneticmaterial. In some embodiments, the powder can be pre-treated tode-oxidize it. In some embodiments, other elements or compounds can beadded to compensate or modify the chemistry of the powder. In someembodiments, the powder can be de-dusted to remove fines. In someembodiments, no pre-processing may be performed.

In some embodiments, the previously used powder can be modified to makeit more applicable as the feedstock as the previous processing can makethe powder/particles unusable. In some embodiments, “satellites”, whichcan hurt/reduce flow can be removed. Further, used powder can becomeagglomerated, and the disclosed process can separate the particles inthe powder. In some embodiments, contaminants, such as organics, can beremoved. In some embodiments, carbon, nitrogen, oxygen, and hydrogen canbe removed from the previously used powder by the disclosed process. Insome embodiments, artifacts can be removed. The disclosed process canalso improve the flowability of the used powders. In some embodiments,surface texture can be adjusted to reduce surface roughness of usedpowder to improve flowability. In some embodiments, flowability can beimproved by absorbing satellites. In some embodiments, residence timeand power levels can be modified to absorb satellites or evaporate them,such as with minimal affect the chemistry of the bulk powders.

Generally, embodiments of the disclosed methods can make the usedpowered spherical again, for example a powder having particles that werespherical and have become not spherical during a previous process. Theseprevious processes can include, but are not limited to, to laser bedfusion, electron-beam melting, and binder jetting. In some embodiments,the used powder can be larger powder waste from an electron beamprocess, which can then be made into a smaller powder for laserapplication. In some embodiments, after use, the powder hasagglomerations, increased oxygen content that is out of specification,contamination from soot and inorganic materials, and/or deformationwhich makes them non-spherical. In these embodiments, the powders cannotbe reused without processing.

In some embodiments, PSD is with a minimum diameter of 1 micrometers(μm) and a maximum diameter of 22 μm, or a minimum of 5 μm and a maximumof 15 μm, or a minimum of 15 μm and a maximum of 45 μm or a minimum of22 μm and a maximum of 44 μm, or a minimum of 20 μm to a maximum of 63μm, or a minimum of 44 μm and a maximum of 70 μm, or a minimum of 70 μmand a maximum of 106 μm, or a minimum of 105 μm to a maximum of 150 μm,or a minimum of 106 μm and a maximum of 300 μm. As will be appreciated,these upper and lower values are provided for illustrative purposesonly, and alternative PSD values may be used in other embodiments. Insome embodiments, the disclosed processing methods retains alloyelements especially highly volatile elements such as Al, Mg, Ti, and Cufrom the used powder.

This disclosure describes the rejuvenation of used powders describedabove to produce fresh powders with improved specifications. Themicrowave plasma process that is made of a microwave generated plasma isused to rejuvenate used powders described above to betterspecifications, so they can be used again as feedstock to the powdermetallurgy processes described above.

In some embodiments, through the processing of used powders, theparticle size distribution can be maintained. In some embodiments, theparticle size distribution can be improved/tightened by absorbingsatellites. In some embodiments, the particle size distribution can beimproved/tightened by re-spheroidizing large agglomerates. For example,for laser powder bed with 15-45 micron particle size distribution, usedpowder can include a) 5% by weight of satellites that are absorbed orevaporated by the microwave plasma process, and b) large misshapenagglomerations, both of which can be removed by embodiments of thedisclosed process. As an example, powders having a particle sizedistribution of 45-106 micron can be reduced to 15-45 micron, such asfor laser powder bed. In some embodiments, the particle sizedistribution can be the D50 of the particles in the powder.

In some embodiments, through the processing of used powders, theparticle size diameter can be altered. In some embodiments, the particlesize diameter can be reduced. In some embodiments, the particle sizediameter can be reduced to produce smaller diameter particle size bypartially vaporizing the surface of large particles. For example, powderfrom an e-beam powder bed with 45-106 micron particle size diameter canbe used to produce powder with 15-45 micron particle size to be used ina laser bed additive manufacturing process.

The plasma gases can be specific to the materials of the powders. As anexample, in the case of metal and metal alloys that do not readily formnitrides, nitrogen gas can be used. One example is the processing ofInconel 718 where when it is run in a nitrogen plasma environment, theprocessed powder is not chemically altered and do not present anynitrogen incorporation into the bulk powder.

In the case of metals and metal alloys that readily react with nitrogen,noble gases such as argon, argon/helium mixture can be used. Also thesenoble gases can be mixed with hydrogen gas to increase the uniformity ofthe plasma. An example of a metal alloy that is susceptible to reactionwith nitrogen is titanium alloy Ti 6% Al-4% V (by weight).

In some instances, noble gases and mixtures such as argon a andargon/hydrogen mixtures are used to avoid any reaction between thepowders and the plasma gases. In other instances, nitrogen can be usedwhen the processed powder is not reactive with the above mentioned gas.

The reconditioning of the used powder/particles can include the removalof artifacts, such as from a laser sintering process. Further,satellites and agglomerated materials due to overheating, for examplefrom a laser process outside a build line, can be removed. Theparticular process to form the used particles, such as additiveprocesses, powder bed fusion, and binder jetting, is not limiting andother processes could have been performed on the original particles.

The reconditioning of the used powder/particles can allow thepowder/particles to, in some embodiments, regain their originalrheological properties (such as bulk density, flowability, etc.). Infact, in some embodiments, the reconditioning of used powder/particlescan also improve the rheological properties. This can be achievedthrough the removing of any satellite on the surface through surfacemelting of the satellites and their incorporation into the bulk of theparticle. In some cases, full melting of the particles will densifyparticles and remove any porosity. Full melting of the particles can beachieved through higher powder density of the plasma and longerresidence time. Also the fact of spheroidizing the powders increasestheir flowability. Angular shaped powders are very hard to flow andtheir flowability increases as their shape becomes more spherical. FIG.6 and FIG. 7 illustrates a sample of CoCr which includes satellitesbefore processing. FIG. 8 and FIG. 9 illustrates a sample of CoCr aftermicrowave plasma processing in which satellites are removed which canimprove flowability by 25% (or by about 25%). FIG. 6 and FIG. 8 show thesame powder before and after microwave plasma processing, respectively.Similarly, FIG. 7 and FIG. 9 show the same powder before and aftermicrowave plasma processing, respectively. In some embodiments,satellites can be absorbed into larger particles.

A satellite can be a main powder particle that has a size that is withinthe defined particle size distribution to which a small particle of muchsmaller diameter that is outside the particle size distribution than thediameter of the main particle is agglomerated either through sinteringor other physical processes.

An agglomeration can be two or more particles which coalesce to form alarger particle.

Further, the reconditioning can minimize oxygen pickup during thereconditioning. This can be achieved by, for example, adding hydrogen orreducing agent, running in a close environment, or running at a hightemperature. In some embodiments, atmospheric pressure inert gas can beused. In some embodiments, a low oxygen environment can be used.

In some embodiments, the alloying component chemistry or minor componentchemistry may not be altered. In some embodiments, certain elements withlow melting temperatures can be removed from the powder.

In some embodiments, the previously used powder particles can be metalor metal alloys. In some embodiments, the previously used powderparticles can be titanium or titanium alloys. Specific titanium that canbe used is Ti (known as CpTi), TiAl, Ti-6-4, and the particular titaniummaterial/alloy does not limit the disclosure. Other materials can beused as well, for example other ductile materials. In some embodiments,nickel and nickel alloys, cobalt, and cobalt alloys, steel, or stainlesssteel can be the previously used powder particles and the particularmaterial is not limiting. In some embodiments, nickel metals/alloys,such as Iconel 718 and 625 superalloys, can be used. In someembodiments, YSZ, MY, CoO, Al₂O₃—TiO₂, Stainless 316L, and 17-4 can beused.

As discussed above, used powder may be extremely complicated to preparefor a feedstock.

Sphericity

In some embodiments, the final particles achieved by the plasmaprocessing can be spherical or spheroidal, terms which can be usedinterchangeably. Advantageously, by using the critical and specificdisclosure relevant to each of the different feedstocks disclosed, allof the feedstocks can be transformed into the spherical powders.

Embodiments of the present disclosure are directed to producingparticles that are substantially spherical or spheroidal or haveundergone significant spheroidization. In some embodiments, spherical,spheroidal or spheroidized particles refer to particles having asphericity greater than a certain threshold. Particle sphericity can becalculated by calculating the surface area of a sphere A_(s,ideal) witha volume matching that of the particle, V using the following equation:

$r_{ideal} = \sqrt[\text{?}]{\frac{3\text{?}}{4\text{?}}}$λ_(s, ideal) = 4π r_(ideal)²?indicates text missing or illegible when filed                    

and then comparing that idealized surface area with the measured surfacearea of the particle, A_(s,actual):

${Sphericity} = {\frac{A_{s,{ideal}}}{A_{s,{actual}}}.}$

In some embodiments, particles can have a sphericity of greater than0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (or greater thanabout 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about 0.8, about0.91, about 0.95, or about 0.99). In some embodiments, particles canhave a sphericity of 0.75 or greater or 0.91 or greater (or about 0.75or greater or about 0.91 or greater). In some embodiments, particles canhave a sphericity of less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91,0.95, or 0.99 (or less than about 0.5, about 0.6, about 0.7, about 0.75,about 0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In someembodiments, a particle is considered to be spherical, spheroidal orspheroidized if it has a sphericity at or above any of theaforementioned sphericity values, and in some preferred embodiments, aparticle is considered to be spherical if its sphericity is at or about0.75 or greater or at or about 0.91 or greater.

In some embodiments, a median sphericity of all particles within a givenpowder can be greater than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or0.99 (or greater than about 0.5, about 0.6, about 0.7, about 0.75, about0.8, about 0.8, about 0.91, about 0.95, or about 0.99). In someembodiments, a median sphericity of all particles within a given powdercan be less than 0.5, 0.6, 0.7, 0.75, 0.8, 0.9, 0.91, 0.95, or 0.99 (orless than about 0.5, about 0.6, about 0.7, about 0.75, about 0.8, about0.8, about 0.91, about 0.95, or about 0.99). In some embodiments, apowder is considered to be spheroidized if all or a threshold percentage(as described by any of the fractions below) of the particles measuredfor the given powder have a median sphericity greater than or equal toany of the aforementioned sphericity values, and in some preferredembodiments, a powder is considered to be spheroidized if all or athreshold percentage of the particles have a median sphericity at orabout 0.75 or greater or at or about 0.91 or greater.

In some embodiments, the fraction of particles within a powder that canbe above a given sphericity threshold, such as described above, can begreater than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or greater than about50%, about 60%, about 70%, about 80%, about 90%, about 95%, or about99%). In some embodiments, the fraction of particles within a powderthat can be above a given sphericity threshold, such as described above,can be less than 50%, 60%, 70%, 80%, 90%, 95%, or 99% (or less thanabout 50%, about 60%, about 70%, about 80%, about 90%, about 95%, orabout 99%).

Particle size distribution and sphericity may be determined by anysuitable known technique such as by SEM, optical microscopy, dynamiclight scattering, laser diffraction, manual measurement of dimensionsusing an image analysis software, for example from about 15-30 measuresper image over at least three images of the same material section orsample, and any other techniques.

In some embodiments, only problematic particles (“bad particles”) areused in the disclosed process. For example, the problematic particlescan be separated from particles that could be used as a feedstock forthe microwave plasma process without any further processing (“goodparticles”). In some embodiments, both the good and the bad particlescan be put into the process.

Powder metallurgy processes such as additive manufacturing, thermal andcold spray coating produce a large amount of waste powders. In someinstances, those powders' morphology is changed from the original freshpowders and can include satellites, partial melting and/or othercontaminants. Those changes can lead to a deterioration of the powderflowability, tap and bulk density, and sometime contamination such ascarbon and nitrogen, and render the used powders useless for the sameprocesses. Recycling those used powders to their original specificationscan provide an economical advantage and lower costs.

In some embodiments that involve used parts, the used parts may bepre-processed before they are introduced into the plasma process. Forexample, the used parts may be sieved to remove large agglomerations andselected to the desired size to be processed in the plasma. In someembodiments, the used parts may be cleaned with water, surfactant,detergent, solvent or any other chemical such as acids to removecontamination. In some embodiments, the used parts may be magneticallycleaned if they are contaminated with any magnetic material. In someembodiments, the used parts can be pre-treated to de-oxidize it. In someembodiments, other elements or compounds can be added to compensate ormodify the chemistry of the used parts. In some embodiments, the usedparts can be de-dusted to remove fines. In some embodiments, nopre-processing may be performed. All of these pre-processing techniquescan also be used on the post-milled powder.

In some embodiments where the material is milled, the material to bemilled can be titanium or titanium alloys. Specific titanium that can beused is Ti (known as CpTi), TiAl, Ti-6-4, and the particular titaniummaterial/alloy does not limit the disclosure. Titanium can be particularproblematic for milling as it is highly ductile, and thus would merelybend or change shape, and would not be broken down properly into apowder without embrittling, such as through hydrogenation or cryogenics.However, embodiments of the disclosure can mill titanium or titaniumalloys without such an embrittling process. This can be done through theunderstanding and proper selection of the scrap material to be milled,such as by only choosing material having a particular volume/size/aspectratio.

Other materials can be used as well, for example other ductilematerials. In some embodiments, nickel and nickel alloys, steel,stainless steel, copper, copper alloys, and Hastealloy can be used andthe particular material is not limiting. In some embodiments, nickelmetals/alloys, such as Iconel 718 and 625 superalloys, can be used. Insome embodiments, oxygen content of the material needs to be in therange of a few ppm to about 2% in the case of reactive materials and afew ppm to about 1% for non-reactive materials.

In some embodiments where the material is milled, the materials can comeinto the milling procedure having particular advantageous properties,such as a work-hardened microstructure. Embodiments of the disclosureallow for the work-hardened microstructure to last all the way throughthe microwave plasma processing, thereby forming a final spheroidizedpowder product retaining the work-hardened material. This can be done byonly microwave plasma processing the outer surface of the particles,thereby retaining the internal work-hardened microstructure. However, insome embodiments the microwave plasma processing heats/melts theparticles all the way through to change the microstructure from what itoriginally was.

For example, work hardened metals and metal alloys feedstock can bespheroidized without affecting the microstructure by a high heating ratethat will only melt the surface of the particles without affecting thebulk, hence preserving the microstructure. The feedstock materials canbe turnings that have been hardened during the machining process, orlarge scrap pieces made of hardened material and that is milled to thedesired size to be used as feedstock for the spheroidization process.

In some embodiments where the material is milled, a miller can determinethe thickness of materials that can be milled based on the prescribeddesired volume.

Accordingly, in some embodiments of the disclosure a user can performthe selection of pieces of ductile material that can be milled to adesired volume without embrittling the material, and then milling thematerial without having to embrittle first to produce particles eachhaving the desired volume as feed material for the microwave plasmatorch. The user can then introduce the particles into the plasma torchand process the powder to retain work hardened microstructure while itspheroidal.

In some embodiments that involve scrap materials, scrap material made ofductile metals and/or metal alloys is milled in a process to avoid thematerial hardening. The ductile product of the milling process is thensieved to different size distributions to be used as feedstock forspheroidization in the microwave plasma melting process. To preserve theductility of the feedstock particles, the heating and cooling rates canbe controlled through the residence time of the particles in the plasmaand in the plasma afterglow.

Embodiments of the disclosed process can include feeding the powdersusing a powder feeder into a microwave generated plasma where the powerdensity, gas flows and residence time are controlled. The processparameters such as power density, flow rates and residence time of thepowder in the plasma can depend on the powder material's physicalcharacteristics, such as the melting point and thermal conductivity. Thepower density can range from 20 W/cm³ to 500 W/cm³ (or about 20 W/cm³ toabout 500 W/cm³). The total gas flows can range from 0.1 cfm to 50 cfm(or about 0.1 cfm to about 50 cfm), and the residence time can be tunedfrom 1 ms to 10 sec (or about 1 ms to about 10 sec). This range ofprocess parameters will cover the required processing parameters formaterials with a wide range of melting point and thermal conductivity.

In some embodiments that involve scrap materials, the scrap material canbe material that is direct from the factory floor. In some embodiments,any remaining contaminants, such as oils, grease, or other material, canbe removed before or during the disclosed process (either prior tomilling, during milling, or during the microwave plasma melting).

In some embodiments, the ability to control oxygen can provideadvantages, for example in the case of titanium scrap.

In some embodiments where the material is milled, the milling can bedone in water. Thus, as the titanium is sheared apart fresh titaniumsurfaces oxidize, which increases the oxygen level.

Different environmental gasses can be used for different applications.As an example, in the case of metal and metal alloys that do not readilyform nitrides, nitrogen gas can be used. One example is the processingof Inconel 718 where when it is run in a nitrogen plasma environment,the processed powder is not chemically altered and do not present anynitrogen incorporation into the bulk powder.

In some embodiments, the feedstock could be of various morphology suchas angular powder, angular chips, irregular powder, and sponge powders.The feedstock can be processed to meet certain criteria for size, gascontent, purity contamination and chemistry by processing such as butnot limited to grinding, milling, cleaning, washing, drying andscreening. The cleaning includes removing organic, ceramic, or othermetallic contaminants.

In some embodiments, nickel or nickel alloys, steel or steel alloys,cobalt or cobalt alloys, and titanium or titanium alloys can be used inembodiments of the disclosure, and the particular material is notlimiting. In some embodiments, ceramics can be used.

In the case of metals and metal alloys that readily react with nitrogen,noble gases such as argon, argon/helium mixture can be used. Also thesenoble gases can be mixed with hydrogen gas to increase the uniformity ofthe plasma. An example of a metal alloy that is susceptible to reactionwith nitrogen is titanium alloy Ti 6% Al-4% V (by weight).

Microwave Plasma Processing

The process parameters can be optimized to obtain maximumspheroidization depending on the feedstock initial condition. For eachfeedstock characteristic, process parameters can be optimized for aparticular outcome. U.S. Pat. Pub. No. 2018/0297122, U.S. Pat. No.8,748,785 B2, and U.S. Pat. No. 9,932,673 B2 disclose certain processingtechniques that can be used in the disclosed process, specifically formicrowave plasma processing. Accordingly, U.S. Pat. Pub. No.2018/0297122, U.S. Pat. No. 8,748,785 B2, and U.S. Pat. No. 9,932,673 B2are incorporated by reference in its entirety and the techniquesdescribes should be considered to be applicable to the feedstockdescribed herein.

One aspect of the present disclosure involves a process ofspheroidization of metals and metal alloys using a microwave generatedplasma. The powder feedstock is entrained in an inert and/or reducinggas environment and injected into the microwave plasma environment. Uponinjection into a hot plasma (or plasma plume or exhaust), the feedstockis spheroidized and released into a chamber filled with an inert gas anddirected into hermetically sealed drums where is it stored. This processcan be carried out at atmospheric pressure, in a partial vacuum, or at aslightly higher pressure than atmospheric pressure. In alternativeembodiments, the process can be carried out in a low, medium, or highvacuum environment. The process can run continuously and the drums arereplaced as they fill up with spheroidized metal or metal alloyparticles.

The rate of cooling of the spheroidized metal and metal alloys can becontrolled to strategically influence the microstructure of the powder.For example, rapid cooling of α-phase titanium alloys facilitates anacicular (martensite) structure. Moderate cooling rates produce aWidmanstätten microstructure, and slow cooling rates form an equiaxedmicrostructure. By controlling the process parameters such as coolinggas flow rate, residence time, cooling gas composition etc.,microstructure of the metal and metal alloys can be controlled. Theprecise cooling rates required to form these structures is largely afunction of the type and quantity of the alloying elements within thematerial.

The rate of cooling, especially when combined with the consistent anduniform heating capabilities of a microwave plasma plume, allow forcontrol over the final microstructure. As a result, the above methodscan be applied to processing metal (e.g., titanium and titanium alloyssuch as Ti 6-4) feedstock. For example, while certain methods may use ametal hydride feedstock, the control over microstructure is not limitedthereto. In particular, the method and powders created by the presenttechnology include the use of non-hydrided sources. For example,titanium metal and various titanium metal alloys can be utilized as thefeedstock source. These materials can be crushed or milled to createparticles for treatment within a microwave plasma torch.

Cooling processing parameters include, but are not limited to, coolinggas flow rate, residence time of the spheroidized particles in the hotzone, and the composition or make of the cooling gas. For example, thecooling rate or quenching rate of the particles can be increased byincreasing the rate of flow of the cooling gas. The faster the coolinggas is flowed past the spheroidized particles exiting the plasma, thehigher the quenching rate-thereby allowing certain desiredmicrostructures to be locked-in. Residence time of the particles withinthe hot zone of the plasma can also be adjusted to provide control overthe resulting microstructure. That is, the length of time the particlesare exposed to the plasma determines the extent of melting of theparticle (i.e., surface of the particle melted as compared to the innermost portion or core of the particle). Consequently, the extent ofmelting effects the extent of cooling needed for solidification and thusit is a cooling process parameter. Microstructural changes can beincorporated throughout the entire particle or just a portion thereofdepending upon the extent of particle melting. Residence time can beadjusted by adjusting such operating variables of particle injectionrate and flow rate (and conditions, such as laminar flow or turbulentflow) within the hot zone. Equipment changes can also be used to adjustresidence time. For example, residence time can be adjusted by changingthe cross-sectional area of the hot zone.

Another cooling processing parameter that can be varied or controlled isthe composition of the cooling gas. Certain cooling gases are morethermally conductive than others. For example helium is considered to bea highly thermally conductive gas. The higher the thermal conductivityof the cooling gas, the faster the spheroidized particles can becooled/quenched. By controlling the composition of the cooling gas(e.g., controlling the quantity or ratio of high thermally conductivegasses to lesser thermally conductive gases) the cooling rate can becontrolled.

As is known in metallurgy, the microstructure of a metal is determinedby the composition of the metal and heating and cooling/quenching of thematerial. In the present technology, by selecting (or knowing) thecomposition of the feedstock material, and then exposing the feedstockto a plasm that has the uniform temperature profile and control thereover as provided by the microwave plasma torch, followed by selectingand controlling the cooling parameters control over the microstructureof the spheroidized metallic particle is achieved. In addition, thephase of the metallic material depends upon the compositions of the feedstock material (e.g., purity, composition of alloying elements, etc.) aswell thermal processing. Titanium has two distinct phases known as thealpha phase (which has a hexagonal close packed crystal structure) and abeta phase which has a body centered cubic structure. Titanium can alsohave a mixed α+β phase. The different crystal structures yield differentmechanical responses. Because titanium is allotropic it can be heattreated to yield specific contents of alpha and beta phases. The desiredmicrostructure is not only a description of the grains (e.g.,martensitic vs. equiaxed) but also the amount and location of differentphases throughout.

In one exemplary embodiment, inert gas is continually purged surroundinga powdered metal feed to remove oxygen within a powder-feed hopper. Acontinuous volume of powder feed is then entrained within an inert gasand fed into the microwave generated plasma for dehydrogenation or forcomposition/maintaining purity of the spheroidized particles. In oneexample, the microwave generated plasma may be generated using amicrowave plasma torch, as described in U.S. Patent Publication No. US2013/0270261, and/or U.S. Pat. Nos. 8,748,785, 9,023,259, 9,259,785, and9,206,085, each of which is hereby incorporated by reference in itsentirety. In some embodiments, the particles are exposed to a uniformtemperature profile at between 4,000 and 8,000 K within the microwavegenerated plasma. In some embodiments, the particles are exposed to auniform temperature profile at between 3,000 and 8,000 K within themicrowave generated plasma. Within the plasma torch, the powderparticles are rapidly heated and melted. Liquid convection acceleratesH₂ diffusion throughout the melted particle, continuously bringinghydrogen (H₂) to the surface of the liquid metal hydride where it leavesthe particle, reducing the time each particle is required to be withinthe process environment relative to solid-state processes. As theparticles within the process are entrained within an inert gas, such asargon, generally contact between particles is minimal, greatly reducingthe occurrence of particle agglomeration. The need for post-processsifting is thus greatly reduced or eliminated, and the resultingparticle size distribution could be practically the same as the particlesize distribution of the input feed materials. In exemplary embodiments,the particle size distribution of the feed materials is maintained inthe end products.

Within the plasma, plasma plume, or exhaust, the melted metals areinherently spheroidized due to liquid surface tension. As the microwavegenerated plasma exhibits a substantially uniform temperature profile,more than 90% spheroidization of particles could be achieved (e.g., 91%,93%, 95%, 97%, 99%, 100%). After exiting the plasma, the particles arecooled before entering collection bins. When the collection bins fill,they can be removed and replaced with an empty bin as needed withoutstopping the process.

In one exemplary embodiment, inert gas is continually purged surroundinga powdered metal feed to remove oxygen within a powder-feed hopper. Acontinuous volume of powder feed is then entrained within an inert gasand fed into the microwave generated plasma for composition/maintainingpurity of the spheroidized particles. In one example, the microwavegenerated plasma may be generated using a microwave plasma torch, asdescribed in U.S. Patent Publication No. US 2013/0270261, and/or U.S.Pat. No. 8,748,785, each of which is hereby incorporated by reference inits entirety. In some embodiments, the particles are exposed to auniform temperature profile at between 4,000 and 8,000 K within themicrowave generated plasma. Within the plasma torch, the powderparticles are rapidly heated and melted. As the particles within theprocess are entrained within an inert gas, such as argon, generallycontact between particles is minimal, greatly reducing the occurrence ofparticle agglomeration. The need for post-process sifting is thusgreatly reduced or eliminated, and the resulting particle sizedistribution could be practically the same as the particle sizedistribution of the input feed materials. In exemplary embodiments, theparticle size distribution of the feed materials is maintained in theend products.

Within the plasma, the melted metals are inherently spheroidized due toliquid surface tension. As the microwave generated plasma exhibits asubstantially uniform temperature profile, more than 90% spheroidizationof particles could be achieved (e.g., 91%, 93%, 95%, 97%, 99%, 100%). Inembodiments, both spheroidization and tailoring (e.g., changing,manipulating, controlling) microstructure are addressed or, in someinstances, partially controlled, by treating with the microwavegenerated plasma. After exiting the plasma, the particles are cooledbefore entering collection bins. When the collection bins fill, they canbe removed and replaced with an empty bin as needed without stopping theprocess.

FIG. 10 is a flow chart illustrating an exemplary method (250) forproducing spherical powders, according to an embodiment of the presentdisclosure. In this embodiment, the process (250) begins by introducinga feed material into a plasma torch (255). In some embodiments, theplasma torch is a microwave generated plasma torch or an RF plasmatorch. Within the plasma torch, the feed materials are exposed to aplasma causing the materials to melt, as described above (260). Themelted materials are spheroidized by surface tension, as discussed above(260 b). After exiting the plasma, the products cool and solidify,locking in the spherical shape and are then collected (265).

As discussed above, the plasma torch can be a microwave generated plasmaor an RF plasma torch. In one example embodiment, an AT-1200 rotatingpowder feeder (available from Thermach Inc.) allows a good control ofthe feed rate of the powder. In an alternative embodiment, the powdercan be fed into the plasma using other suitable means, such as afluidized bed feeder. The feed materials may be introduced at a constantrate, and the rate may be adjusted such that particles do notagglomerate during subsequent processing steps. In another exemplaryembodiment, the feed materials to be processed are first sifted andclassified according to their diameters, with a minimum diameter of 1micrometers (μm) and a maximum diameter of 22 μm, or a minimum of 5 μmand a maximum of 15 μm, or a minimum of 15 μm and a maximum of 45 μm ora minimum of 22 μm and a maximum of 44 μm, or a minimum of 20 μm to amaximum of 63 μm, or a minimum of 44 μm and a maximum of 70 μm, or aminimum of 70 μm and a maximum of 106 μm, or a minimum of 105 μm to amaximum of 150 μm, or a minimum of 106 μm and a maximum of 300 μm. Aswill be appreciated, these upper and lower values are provided forillustrative purposes only, and alternative size distribution values maybe used in other embodiments. This eliminates recirculation of lightparticles above the hot zone of the plasma and also ensures that theprocess energy present in the plasma is sufficient to melt the particleswithout vaporization. Pre-screening allows efficient allocation ofmicrowave power necessary to melt the particles without vaporizingmaterial.

In some embodiments, the environment and/or sealing requirements of thebins are carefully controlled. That is, to prevent contamination orpotential oxidation of the powders, the environment and or seals of thebins are tailored to the application. In one embodiment, the bins areunder a vacuum. In one embodiment, the bins are hermetically sealedafter being filled with powder generated in accordance with the presenttechnology. In one embodiment, the bins are back filled with an inertgas, such as, for example argon. Because of the continuous nature of theprocess, once a bin is filled, it can be removed and replaced with anempty bin as needed without stopping the plasma process.

The methods and processes in accordance with the disclosure can be usedto make spherical metal powders or spherical metal alloy powders. Forexample, if the starting feed material is a titanium material, theresulting powder will be a spherical titanium powder. If the startingfeed material is a titanium alloy material, the resulting powder will bea spherical titanium alloy powder. In one embodiment that features theuse of a starting titanium alloy material, the resulting sphericaltitanium alloy powder comprises spherioidized particles of Ti Al6-V4,with between 4% to 7% weight aluminum (e.g., 5.5 to 6.5% Al) (or about4% to about 7%, or about 5.5% to about 6.5%) and 3% to 5% weightvanadium (e.g., 3.5 to 4.5% vanadium) (or about 3% to about 5%, or about3.5 to about 4.5%). In some embodiments, the material may have acomposition that is within 10% (+/−10%) of the wt. % listed in thisparagraph. In some embodiments, the feed material may be Ti Al6-V4 (orTi-6-4) and wherein the melting and spheroidizing is controlled suchthat the spheroidized powder comprises Ti Al6-V4 as discussed herein.E.g., in some embodiments both the initial feedstock and the finalpowder is Ti Al6-V4. In some embodiments, the starting feedstock andfinal powder can have a different composition, but still be within theTi Al6-V4 discussed herein. In some embodiments, the starting feedstockand final powder can have a different composition.

In some embodiments, the processing discussed herein, such as themicrowave plasma processing, can be controlled to prevent and/orminimize aluminum for escaping the feedstock during the melt, which canmaintain the desired composition/microstructure.

FIG. 11 illustrates an exemplary microwave plasma torch that can be usedin the production of spheroidal metal or metal alloy powders, accordingto embodiments of the present disclosure. As discussed above, metal feedmaterials 9, 10 can be introduced into a microwave plasma torch 3, whichsustains a microwave generated plasma 11. In one example embodiment, anentrainment gas flow and a sheath flow (downward arrows) may be injectedthrough inlets 5 to create flow conditions within the plasma torch priorto ignition of the plasma 11 via microwave radiation source 1. In someembodiments, the entrainment flow and sheath flow are bothaxis-symmetric and laminar, while in other embodiments the gas flows areswirling. The feed materials 9 are introduced axially into the microwaveplasma torch, where they are entrained by a gas flow that directs thematerials toward the plasma. As discussed above, the gas flows canconsist of a noble gas column of the periodic table, such as helium,neon, argon, etc. Within the microwave generated plasma, the feedmaterials are melted in order to spheroidize the materials. Inlets 5 canbe used to introduce process gases to entrain and accelerate particles9, 10 along axis 12 towards plasma 11. First, particles 9 areaccelerated by entrainment using a core laminar gas flow (upper set ofarrows) created through an annular gap within the plasma torch. A secondlaminar flow (lower set of arrows) can be created through a secondannular gap to provide laminar sheathing for the inside wall ofdielectric torch 3 to protect it from melting due to heat radiation fromplasma 11. In exemplary embodiments, the laminar flows direct particles9, 10 toward the plasma 11 along a path as close as possible to axis 12,exposing them to a substantially uniform temperature within the plasma.In some embodiments, suitable flow conditions are present to keepparticles 10 from reaching the inner wall of the plasma torch 3 whereplasma attachment could take place. Particles 9, 10 are guided by thegas flows towards microwave plasma 11 were each undergoes homogeneousthermal treatment. Various parameters of the microwave generated plasma,as well as particle parameters, may be adjusted in order to achievedesired results. These parameters may include microwave power, feedmaterial size, feed material insertion rate, gas flow rates, plasmatemperature, residence time and cooling rates. In some embodiments, thecooling or quenching rate is not less than 10⁺³ degrees C./sec uponexiting plasma 11. As discussed above, in this particular embodiment,the gas flows are laminar; however, in alternative embodiments, swirlflows or turbulent flows may be used to direct the feed materials towardthe plasma.

FIGS. 12A-B illustrates an exemplary microwave plasma torch thatincludes a side feeding hopper rather than the top feeding hopper shownin the embodiment of FIG. 11, thus allowing for downstream feeding.Thus, in this implementation the feedstock is injected after themicrowave plasma torch applicator for processing in the “plume” or“exhaust” of the microwave plasma torch. Thus, the plasma of themicrowave plasma torch is engaged at the exit end of the plasma torch toallow downstream feeding of the feedstock, as opposed to the top-feeding(or upstream feeding) discussed with respect to FIG. 11. This downstreamfeeding can advantageously extend the lifetime of the torch as the hotzone is preserved indefinitely from any material deposits on the wallsof the hot zone liner. Furthermore, it allows engaging the plasma plumedownstream at temperature suitable for optimal melting of powdersthrough precise targeting of temperature level and residence time. Forexample, there is the ability to dial the length of the plume usingmicrowave powder, gas flows, and pressure in the quenching vessel thatcontains the plasma plume. Additionally, the downstream approach mayallow for the use of wire feedstocks instead to produce spheroidizedmaterials such as metals which may include aluminum, Iconel, titanium,molybdenum, tungsten, and rhenium. This spheroidization method can beapplied to both ceramics and metals.

Generally, the downstream spheroidization method can utilize two mainhardware configurations to establish a stable plasma plume which are:annular torch, such as described in U.S. Pat. Pub. No. 2018/0297122, orswirl torchas described in U.S. Pat. No. 8,748,785 B2 and U.S. Pat. No.9,932,673 B2. Both FIG. 12A and FIG. 12B show embodiments of a methodthat can be implemented with either an annular torch or a swirl torch. Afeed system close-coupled with the plasma plume at the exit of theplasma torch is used to feed powder axisymmetrically to preserve processhomogeneity. Other feeding configurations may include one or severalindividual feeding nozzles surrounding the plasma plume. The feedstockpowder can enter the plasma from any direction and can be fed in 360°around the plasma. The feedstock powder can enter the plasma at aspecific position along the length of the plasma plume where a specifictemperature has been measured and a residence time estimated forsufficient melting of the particles. The melted particles exit theplasma into a sealed chamber where they are quenched then collected.

The metal feed materials 314 can be introduced into a microwave plasmatorch 302. A hopper 306 can be used to store the metal feed material 314before feeding the metal feed material 314 into the microwave plasmatorch 302, plume, or exhaust. The feed material 314 can be injected atany angle to the longitudinal direction of the plasma torch 302. 5, 10,15, 20, 25, 30, 35, 40, 45, 50, or 55 degrees. In some embodiments, thefeedstock can be injected an angle of greater than 5, 10, 15, 20, 25,30, 35, 40, 45, 50, or 55 degrees. In some embodiments, the feedstockcan be injected an angle of less than 5, 10, 15, 20, 25, 30, 35, 40, 45,50, or 55 degrees. In alternative embodiments, the feedstock can beinjected along the longitudinal axis of the plasma torch. The microwaveradiation can be brought into the plasma torch through a waveguide 304.The feed material 314 is fed into a plasma chamber 310 and is placedinto contact with the plasma generated by the plasma torch 302. When incontact with the plasma, plasma plume, or plasma exhaust, the feedmaterial melts. While still in the plasma chamber 310, the feed material314 cools and solidifies before being collected into a container 312.Alternatively, the feed material 314 can exit the plasma chamber 310while still in a melted phase and cool and solidify outside the plasmachamber. In some embodiments, a quenching chamber may be used, which mayor may not use positive pressure. While described separately from FIG.11, the embodiments of FIGS. 12A-B are understood to use similarfeatures and conditions to the embodiment of FIG. 11.

In some embodiments, implementation of the downstream injection methodmay use a downstream swirl, extended spheroidization, or quenching. Adownstream swirl refers to an additional swirl component that can beintroduced downstream from the plasma torch to keep the powder from thewalls of the tube. An extended spheroidization refers to an extendedplasma chamber to give the powder longer residence time. In someimplementations, it may not use a downstream swirl, extendedspheroidization, or quenching. In some embodiments, it may use one of adownstream swirl, extended spheroidization, or quenching. In someembodiments, it may use two of a downstream swirl, extendedspheroidization, or quenching.

Injection of powder from below may results in the reduction orelimination of plasma-tube coating in the microwave region. When thecoating becomes too substantial, the microwave energy is shielded fromentering the plasma hot zone and the plasma coupling is reduced. Attimes, the plasma may even extinguish and become unstable. Decrease ofplasma intensity means decreases in spheroidization level of the powder.Thus, by feeding feedstock below the microwave region and engaging theplasma plume at the exit of the plasma torch, coating in this region iseliminated and the microwave powder to plasma coupling remains constantthrough the process allowing adequate spheroidization.

Thus, advantageously the downstream approach may allow for the method torun for long durations as the coating issue is reduced. Further, thedownstream approach allows for the ability to inject more powder asthere is no need to minimize coating.

FIG. 13 illustrates an exemplary method (500) of producing spheroidizedtitanium particles with a tailored or desired microstructure. Method 500includes several processing steps to treat metallic feed materials suchas, for example, titanium feed materials (e.g., titanium or titaniumalloys) to create spheroidized metallic particles with a desiredmicrostructure. In step 510, metallic (e.g., titanium based) feedmaterials comprising particles are feed into a plasma torch. Theparticles can be produced from crushing, pulverizing, or milling feedstock materials. In general, the feed stock particles have an averageparticle size of between 1 micron and 300 microns. In step 515, the feedstock particles are exposed to a microwave generated plasma to melt atleast the surface portion of the particles. The melted portions of theparticles allow for spheriodization of the particles. In step 520, thespheroidized particles are exposed to an inert gas such helium,nitrogen, argon or combinations/mixtures thereof. In step 525, thecooling processing variables/conditions are set and maintained toachieve a desired microstructure. For example, in embodiments in which amartensitic microstructure is desired throughout the entire particle,the cooling processing conditions are set for rapid cooling. As aresult, the residence time of the particles in the hot zone is selectedto allow for melting of the entire feedstock particle, the cooling gasflow rate is set to a fastest rate, and the amount of helium forming thecomposition of the cooling gas is set to a maximum available. Afterexposing the spheroidized particles to the selected cooling conditions,the spherical powders are collected in step 530.

FIG. 14 illustrates an exemplary method (600) of modifying metallic feedstock material to have a spheroidized shape and a desiredmicrostructure. The method of 600 includes several processing steps totreat metallic feed materials such as, for example, titanium feedmaterials (e.g., titanium or titanium alloys) to create spheroidizedmetallic particles with a desired microstructure. In this method,knowledge of the chemical composition of the feed stock (e.g., 99.9%pure titanium, Ti-6Al-4V, etc.) is used in combination with control overthermal processing conditions to achieve spheroidal particles with adesired microstructure different than the metallic feed stock material.In step 610, the composition of the Ti-based feed stock material isselected or analyzed to determine its composition. In step 615, adesired microstructure of a final product is determined. For example, itmay be determined that an α-phase 99% pure Ti equiaxed microstructurethroughout the spheroidized particle is desired. As a result, a slowerrate of cooling will be required than that used to produce a martensiticmicrostructure. Cooling processing parameters will be selected (step620), such as cooling gas flow rate, residence time, and/or compositionof cooling gas to achieve such a microstructure based upon thecomposition of the feed stock materials. In general, the microstructureof the final product will differ from the original feed stock material.That is an advantage of the present method is to be able to efficientlyprocess feed materials to create spheroidized particles with a desiredmicrostructure. After selecting or determining the cooling parameters,the feed stock particles are melted in the microwave generated plasma tospheriodize the particles in step 625. The spheroidized particles areexposed to an inert gas (step 630) and the determined or selectedcooling parameters are applied to form the desired microstructure.

The desired microstructure of the spheroidized particle (end product)can be tailored to meet the demands and material characteristics of itsuse. For example, the desired microstructure may be one that providesimproved ductility (generally associated with the α-phase). In anotherexample, the desired microstructure may be associated with the inclusionof α+β phase or regions of a with islands of (3 phase or vice-versa.Without wishing to be bound by theory, it is believe that the methods ofthe present disclosure allow for control over the phase of thespheroidized particles as the microwave generated plasma has a uniformtemperature profile, fine control over the hot zone, and the ability toselect and adjust cooling processing parameters.

Using the methods of the present technology, various microstructures,crystal structures and regions of differing microstructure and/orcrystal structures can be produced. Accordingly, new spheroidal titaniumparticles can be produced efficiently. For example, due to the abilitiesto control the hot zone and cooling processing parameters, the presenttechnology allows an operator to create multiple regions within thespheroidal particle. FIG. 15 shows such an embodiment. This figureillustrates a spheroidal particle which has two distinct regions. Theouter or shell region 715 and an inner core 710. The original titaniumfeed material for this particle was a pure titanium α-phase powder. Thefeed material was exposed to the plasma under conditions (temperature,residence time, etc.) such that only a surface portion of the particlemelted, so that spheriodization could occur. Cooling rates appliedallowed for the transformation of the shell region to transform toβ-phase, leaving the core to retain the α-phase. In some embodiments,for Ti-6-4, both the shell and the inner core are Ti-6-4. In someembodiments, the core composition/microstructure is retained, such askeeping Ti-6-4, and the shell composition/microstructure can be changed.

In another embodiment, not shown, the entire feed stock particle can bemelted and cooling parameters can be selected and applied to create acrystal structure that has the same phase as the feed stock material(e.g., retains α-phase) or is transformed to a new phase or mixture ofphases. Similarly, cooling processing parameters can be selected andapplied to create spheroidal particles that have the same microstructurethroughout the particle or various microstructures in two or moreregions (e.g., shell region, core region).

From the foregoing description, it will be appreciated that inventiveprocessing methods for converting unique feedstocks to spheroidizedpowder are disclosed. While several components, techniques and aspectshave been described with a certain degree of particularity, it ismanifest that many changes can be made in the specific designs,constructions and methodology herein above described without departingfrom the spirit and scope of this disclosure.

Certain features that are described in this disclosure in the context ofseparate implementations can also be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation can also be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations, one or more features from a claimed combination can, insome cases, be excised from the combination, and the combination may beclaimed as any subcombination or variation of any subcombination.

Moreover, while methods may be depicted in the drawings or described inthe specification in a particular order, such methods need not beperformed in the particular order shown or in sequential order, and thatall methods need not be performed, to achieve desirable results. Othermethods that are not depicted or described can be incorporated in theexample methods and processes. For example, one or more additionalmethods can be performed before, after, simultaneously, or between anyof the described methods. Further, the methods may be rearranged orreordered in other implementations. Also, the separation of varioussystem components in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described components and systems cangenerally be integrated together in a single product or packaged intomultiple products. Additionally, other implementations are within thescope of this disclosure.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include or do not include, certain features, elements,and/or steps. Thus, such conditional language is not generally intendedto imply that features, elements, and/or steps are in any way requiredfor one or more embodiments.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,”“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than or equal to 10% of, within less than or equal to 5% of, withinless than or equal to 1% of, within less than or equal to 0.1% of, andwithin less than or equal to 0.01% of the stated amount. If the statedamount is 0 (e.g., none, having no), the above recited ranges can bespecific ranges, and not within a particular % of the value. Forexample, within less than or equal to 10 wt./vol. % of, within less thanor equal to 5 wt./vol. % of, within less than or equal to 1 wt./vol. %of, within less than or equal to 0.1 wt./vol. % of, and within less thanor equal to 0.01 wt./vol. % of the stated amount.

The disclosure herein of any particular feature, aspect, method,property, characteristic, quality, attribute, element, or the like inconnection with various embodiments can be used in all other embodimentsset forth herein. Additionally, it will be recognized that any methodsdescribed herein may be practiced using any device suitable forperforming the recited steps.

While a number of embodiments and variations thereof have been describedin detail, other modifications and methods of using the same will beapparent to those of skill in the art. Accordingly, it should beunderstood that various applications, modifications, materials, andsubstitutions can be made of equivalents without departing from theunique and inventive disclosure herein or the scope of the claims.

1. (canceled)
 2. A method for manufacturing a metal spheroidized powder,the method comprising: providing a titanium feedstock material to amicrowave plasma torch; and subjecting the titanium feedstock materialto a microwave plasma process within the microwave plasma torch to formthe metal spheroidized powder, the microwave plasma process comprisingintroduction of an ionized plasma into the microwave plasma torch, theionized plasma comprising nitrogen.
 3. The method of claim 2, whereinthe titanium feedstock material comprises titanium powder.
 4. The methodof claim 2, wherein the titanium feedstock material has a particle sizedistribution between 15 microns and 150 microns.
 5. The method of claim2, wherein titanium feedstock material comprises commercially puretitanium (cpTi).
 6. The method of claim 2, wherein titanium feedstockmaterial hydride-dehydride (HDH) titanium powder.
 7. The method of claim2, further comprising entraining the titanium feedstock material with aninert gas within the microwave plasma torch.
 8. The method of claim 2,wherein subjecting the titanium feedstock material to a microwave plasmaprocess comprises introducing the titanium feedstock material to amicrowave generated plasma environment having a temperature profilebetween 4,000 K and 8,000 K.
 9. The method of claim 8, whereinintroducing the titanium feedstock material to the microwave generatedplasma environment melts at least a surface portion of the titaniumfeedstock material.
 10. The method of claim 9, wherein melting at leastthe surface portion of the titanium feedstock material allows forspheroidization of the titanium feedstock material.
 11. The method ofclaim 2, wherein the metal spheroidized powder comprises particles witha median sphericity of at least 0.75.
 12. The method claim 2, whereinthe metal spheroidized powder has a particle size distribution ofbetween 5 and 45 microns at a low end of the particle size distributionrange and between 15 and 105 microns at a high end of the particle sizedistribution range.
 13. The method of claim 2, wherein the metalspheroidized powder comprises particles comprising at least twodifferent microstructures or crystal structures.
 14. The method of claim2, wherein the metal spheroidized powder comprises particles comprisinga core microstructure proximate to an interior region of the particlesand a shell microstructure proximate to an outer region of theparticles.
 15. The method of claim 2, wherein the titanium feedstockmaterial comprises particles comprising an average particle size between1 micron and 300 microns.
 16. The method of claim 2, further comprisingcooling the metal spheroidized powder, the cooling comprisingcontrolling one or more cooling process parameters.
 17. The method ofclaim 16, wherein the one or more cooling process parameters comprise acomposition of a cooling gas, a cooling gas flow rate, and a residencetime of the metal spheroidized powder.
 18. The method of claim 2,further comprising selecting or analyzing the titanium feedstockmaterial to determine the composition of the titanium feedstock materialprior to providing the titanium feedstock material to the microwaveplasma torch.
 19. The method of claim 17, further comprising determininga desired microstructure of the spheroidized metal powder based on thedetermined composition of the titanium feedstock material.
 20. Themethod of claim 2, wherein a particle size distribution of the titaniumfeedstock material is maintained in a particle size distribution of themetal spheroidized powder.
 21. The method of claim 2, further comprisingcollecting the metal spheroidized powder in sealed drums in an inertatmosphere.